Roller nestlings respond to fear and predation threats by vomiting

The beautiful Eurasian Roller is "near-threatened" in western Europe, but increasing its numbers in newly forested areas in eastern Europe. It sits on isolated trees and takes off to capture large insect prey; Credit: Shutterstock

The hormonal adrenalin response is well known to humans. The Eurasian roller, or blue roller (Coracias garrulus) has a much more obvious mechanism for rapid response quite like the foul smelling fulmar's literal stomach turnings. The smelly orange liquid that roller nestlings vomit serves to inform their parents that they have been attacked (as well as put the predators off!) The species concerned in this Spanish paper published in the journal Biology Letters is, as mentioned, the Eurasian roller, Coracias garrulus.

1. 1ml of lemon juice was applied just inside the entrance hole of the box, or

2. 1ml of vomit was similarly applied

The effects were observed and analyses performed by D. Parejo, L.Amo, J. Rodrıguez and J. M. Aviles as follows:

Of particular concern to the four observers was how long the parent took before they entered the nest. They called this "latency." Parents increased their provisioning of the nest when lemon juice was used and decreased it when the vomit was present. They also delayed their entrance.

The olfactory (smell) response to the volatile substances was seen as the only possible stimulus in the experiment, giving some of the first evidence of such a response in birds. The parents were obviously applying caution when the fear response was smelt. As well as showering each other with repellent, the young were informing their parents of possible danger both to themselves and their offspring.

The importance of warnings to parents would increase their own chance of survival as well as that of their offspring. The authors claim that this intra-specific signalling is promising as a research tool, to discover how many olfactory signals could be passed among birds. Interest also lies in the inter-specific nature of the stimulus. It would normally be caused by the rollers' predators, such as a snake or bird of prey. We watch with interest as these most visual of creatures is investigated for sense of smell.

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